Matte Tin, is tin protected with an OSP. The OSP can fail, allowing the tin
to oxidize. The land can become unsolderable. Also the finish can be too
thin to provide the desired protection to the underlying lead frame. The
part probably has a copper lead frame without any nickel.
Some of the parts we get here for qualification have been "conditioned". You
know the drill.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, April 23, 2013 1:41 PM
To: [log in to unmask]
Subject: Re: [TN] QFN Pad Corrosion?
Hi Rueven,
The photo is of the QFN, not the board. The QFN is matte tin finished...
Steve
From: Reuven Rokah [mailto:[log in to unmask]]
Sent: Tuesday, April 23, 2013 11:37 AM
To: TechNet E-Mail Forum; Steve Gregory
Subject: Re: [TN] QFN Pad Corrosion?
PCBs finish are ENIG?
May be black pads?
Reuven
On Tue, Apr 23, 2013 at 8:12 PM, Steve Gregory <[log in to unmask]>
wrote:
Hi All,
I have another question about the QFN16 that I was talking about last
week. I was sent a photo of the bottom of one of the devices after it
had been removed from a failed board. It is here:
http://stevezeva.homestead.com/QFN16_Corrosion.jpg
It's pointing out a pad that seemed to have a lot of corrosion on it and
I was told that solder would not wet to it. I was asked what might cause
this?
My first thoughts are that the appearance might have been caused by the
rework when it was removed, and that a un-solderable intermetallic has
formed on pad but I can't say that for sure. The part is finished with
matte tin when it is supplied. When a part is tin finished, they have a
barrier nickel plate beneath the tin right?
I don't have the part in front of me, I only got sent the photo. I was
asked what my thoughts were, so I thought I'd ask my TechNet friends
too... :o)
Thanks,
Steve Gregory
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